1. Field of the Invention
The present invention pertains to a release system for a clutch assembly, comprising a release slide, which is or can be connected to a stored-energy element of the clutch assembly to execute release movements, and at least one brake element, which is free to move along with the release slide during the execution of the release movements, which brake element can be brought into braking interaction with an opposing brake element which is or can be connected in essentially nonrotatable fashion to a clutch output shaft, where the release slide and the minimum of one brake element form a piston/cylinder unit with at least one fluid chamber.
2. Description of the Related Art
A release system is known from U.S. Pat. No. 4,099,604, in which a brake element is movably connected to a release slide, which can slide in the same direction as that in which a clutch rotational axis extends to execute release movements. If, after the release movement has been executed and the clutch has been completely released, the release slide is moved even farther by appropriate actuation, the brake element is pressed against an opposing brake element, which is connected nonrotatably to a clutch output shaft. As a result, a braking force is exerted on the clutch output shaft and thus on the transmission input shaft. This is advantageous especially when such systems are used in conjunction with unsynchronized transmissions. In order to ensure in an arrangement of this type that, even after the friction linings of the clutch assembly have become worn, the release system and also the brake system provided for the clutch output shaft will still have the same actuating characteristic or working characteristic, a wear compensating mechanism is provided, by means of which a relative displacement occurs between the release slide and the pressure plate upon the occurrence of wear without any change in the original installation position of the stored-energy element. This ensures that the release slide and thus also the braking element will always remain in approximately the same installation position regardless of the amount of wear and that the working characteristics of the braking arrangement for the clutch output shaft will always remain the same during the execution of clutch-release operations.
A release system for a clutch assembly is also known from U.S. Pat. No. 3,912,058, in which a release slide, which can be displaced by the introduction of pressure fluid so that it can execute release movements, can also be used to push a brake element to generate a braking force at least in the situation where the release stroke exceeds a certain value. To take into account the fact here, too, that, as wear occurs, the installation position of the stored-energy element and thus also the base of the release slide can change, the brake element or a part thereof and the release slide form a piston/cylinder unit. This unit has a cylindrical chamber, into which fluid is introduced to an extent corresponding to the amount of wear and thus corresponding to the axial displacement of the release slide. The relative displacement between the release slide and the section of the braking element working together with the slide to form the piston/cylinder unit, which relative displacement occurs as a result of wear, is ultimately compensated by the increase in the volume of the fluid chamber and the filling of this fluid chamber with fluid. In spite of the displacement of the release slide occurring as a result of wear, therefore, the section of the brake element cooperating with it to form the piston/cylinder unit is held in the same axial installation position, so that, for all succeeding clutch-release operations, a uniform working characteristic can be obtained, at least in the area of the system which provides braking force for the clutch output shaft or transmission input shaft.
It is the object of the present invention to provide a release system for a clutch assembly by means of which it is possible to produce a precise amount of braking force for a clutch output shaft or a transmission input shaft.
According to the invention, pressure fluid can be introduced into the minimum of one fluid chamber to produce a force which preloads or moves the minimum of one brake element relative to the release slide.
In contrast to the state of the art, in which the thrust produced by the release slide is transmitted to the brake element by way of the fluid in the fluid chamber to displace the brake element so that it will produce the braking action, the force which is intended to decelerate the transmission input shaft is generated actively in the release system by introducing pressure fluid into the minimum of one fluid chamber. The braking force can thus be generated in almost complete independence of the executed release movement or of the executed release stroke of the release slide, so that a much more precise actuation of the system serving to decelerate the transmission input shaft can be achieved in comparison to an arrangement in which the desired effect is necessarily coupled with the stroke of the release slide. It is possible in particular to achieve a temporary disconnection between the braking operation and the release operation, so that, for example, it is possible to begin building up the braking force even before the clutch has reached the position in which it is completely released, and ultimately there is no phase present in which the transmission input shaft can rotate without being braked.
It is possible, for example, for the pressure fluid which can be introduced into the minimum of one fluid chamber to generate a braking pressure, which presses the minimum of one brake element against the counter-brake element.
So that it is possible to produce a braking characteristic which is uniformly distributed around the circumference, it is proposed that a plurality of cylindrical chambers be provided in the release slide, arranged in sequence in the circumferential direction relative to a rotational axis, and that an associated piston segment of the minimum of one brake element fits into each of these chambers with the freedom to slide. The same result can also be achieved in a different way by providing the release slide with a cylindrical chamber in the shape of a ring surrounding the rotational axis, into which chamber a ring-shaped piston segment of the minimum of one brake element fits with the freedom to slide.
Because the brake element usually remains in approximately the same axial position during the execution of engagement and release operations or at most is not pushed as far in the axial direction as the release slide is, it is proposed that, to simplify the introduction of the pressure fluid into the minimum of one fluid chamber, a pressure fluid feed connection arrangement for the minimum of one fluid chamber be provided on the minimum of one brake element.
In the release system according to the invention, it is preferable to provide a pressure fluid feed arrangement by means of which pressure fluid can be introduced into the minimum of one fluid chamber essentially only when the clutch assembly has been actuated beyond the point associated with the essentially complete release of the clutch.
To avoid undesirable interactions in the area of the brake system during the execution of clutching operations, it is proposed that, upon actuation of the clutch assembly up to the position in which release is essentially complete, essentially no fluid pressure which could produce a displacing force is allowed to build up in the fluid chamber. Nevertheless, it should also be pointed out again that, as a result of the disconnection between the release system and the brake system, it is possible for there to be a certain overlap between the execution of a release operation and the execution of a braking operation, which overlap can be advantageous and desirable under certain conditions.
The present invention also pertains to a drive system with a clutch assembly and a release system according to the invention, where it is also provided that pressure fluid is introduced into the minimum of one fluid chamber only after the clutch assembly has been actuated beyond the point at which release is essentially complete.
It is also advantageous in this release system for there not to be any buildup in the fluid pressure which could produce a displacing force in the minimum of one fluid chamber during the times that the clutch assembly is not being actuated to execute a release movement or during the times that it is being actuated but has not yet reached or has not yet exceeded the essentially complete release actuation position. It is also preferred that the minimum of one fluid chamber be connected to a fluid reservoir or to the outside.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.